Helminths – FRCPath Part 2 Short Notes

1. Trematodes (Flukes)

Schistosoma spp.

• Epidemiology/Geography:
  • S. haematobium → Africa, Middle East.
  • S. mansoni → Africa, Middle East, South America, Caribbean.
  • S. japonicum → China, Philippines, SE Asia.
• Transmission: Skin penetration by cercariae from freshwater snails.
• Clinical:
  • S. haematobium → urinary schistosomiasis, ↑ bladder carcinoma risk.
  • S. mansoni → intestinal + hepatosplenic disease.
  • S. japonicum → more severe hepatosplenic disease.
• Diagnostics: Eggs in stool/urine (terminal vs lateral spines), serology, antigen detection (CCA).
• Treatment: Praziquantel (40 mg/kg).
• Public health: WHO mass drug administration (MDA).

Clonorchis sinensis / Opisthorchis spp.

• Geography: China, Korea, Vietnam, Thailand, Laos, Cambodia.
• Transmission: Ingestion of metacercariae in raw freshwater fish.
• Clinical: Biliary obstruction, cholangitis, cholangiocarcinoma risk.
• Diagnostics: Small operculated eggs in stool.
• Treatment: Praziquantel.

Small operculated egg

Fasciola hepatica

• Epidemiology: Sheep-raising areas worldwide; watercress ingestion.
• Transmission: Ingestion of metacercariae on aquatic plants.
• Clinical: Acute (fever, RUQ pain, eosinophilia); chronic (biliary obstruction).
• Diagnostics: Large operculated eggs in stool, serology.
• Treatment: Triclabendazole (not praziquantel).

Paragonimus westermani

• Epidemiology: Asia; raw/undercooked freshwater crab/crayfish.
• Clinical: Pulmonary infection (cough, haemoptysis, TB mimic); ectopic CNS disease.
• Diagnostics: Operculated eggs in sputum/stool.
• Treatment: Praziquantel.
• 

2. Cestodes (Tapeworms)

Taenia saginata / Taenia solium

• Epidemiology: Worldwide, esp. where beef/pork undercooked.
• Transmission: Ingestion of cysticerci in meat.
• Clinical: Intestinal taeniasis; T. solium → cysticercosis (CNS seizures).
• Diagnostics: Eggs (radial striations), proglottids in stool; neuroimaging + serology for cysticercosis.
• Treatment:
  • Praziquantel/niclosamide (intestinal);
  • albendazole + steroids (neurocysticercosis).

Differences: saginata is cattle, tapeworms longer (up to 10m), unarmed, more uterine branches, intestinal only.

Echinococcus granulosus (dog) / multilocularis (fox)

• Epidemiology: Sheep-raising regions (Mediterranean, Middle East, South America, China).
• Transmission: Ingestion of eggs from dog faeces.
• Clinical: Hydatid cysts (liver, lung); rupture → anaphylaxis; E. multilocularis → invasive hepatic disease.
• Diagnostics: Imaging (US/CT), serology.
• Treatment: Albendazole ± PAIR (puncture-aspiration-injection-reaspiration) or surgery.

Diphyllobothrium latum

• Epidemiology: N. Europe, Japan; raw freshwater fish.
• Clinical: Intestinal tapeworm; B12 deficiency → megaloblastic anaemia.
• Diagnostics: Operculated eggs in stool.
• Treatment: Praziquantel.
• 

Hymenolepis nana

• Epidemiology: Worldwide, esp. children.
• Transmission: Ingestion of eggs; autoinfection possible.
• Clinical: Diarrhoea, abdominal pain.
• Diagnostics: Eggs in stool (polar filaments).
• Treatment: Praziquantel.

3. Nematodes (Roundworms)

Ascaris lumbricoides

• Epidemiology: Most common helminth worldwide.
• Transmission: Ingestion of embryonated eggs in contaminated food/soil.
• Clinical: Loeffler’s pneumonitis (larval migration), intestinal obstruction, biliary colic.
• Diagnostics: Large mammillated eggs in stool.
• Treatment: Albendazole/mebendazole.

Trichuris trichiura (Whipworm)

• Transmission: Ingestion of eggs.
• Clinical: Dysentery, rectal prolapse in heavy infections.
• Diagnostics: Barrel-shaped eggs with bipolar plugs.
• Treatment: Albendazole/mebendazole.

Enterobius vermicularis (Pinworm)

• Epidemiology: Common in children.
• Transmission: Ingestion of eggs (perianal → hand → mouth) > autoinfection
• Clinical: Perianal itch (worse at night).
• Diagnostics: “Scotch tape test.”
• Treatment: Mebendazole; treat household contacts.

Strongyloides stercoralis

• Transmission: Skin penetration by larvae.
• Clinical: Asymptomatic or mild diarrhoea; hyperinfection in immunocompromised (esp. steroids, HTLV-1), associated with Gram negative sepsis
• Diagnostics: Rhabditiform larvae in stool, serology, PCR.
• Treatment: Ivermectin (not albendazole).

Hookworms (Ancylostoma duodenale, Necator americanus)

• Transmission: Skin penetration by larvae.
• Clinical: Iron deficiency anaemia, malnutrition.
• Diagnostics: Thin-shelled eggs in stool.
• Treatment: Albendazole/mebendazole.

Trichinella spiralis

• Transmission: Ingestion of encysted larvae in undercooked pork/wild game.
• Clinical: Myositis, fever, eosinophilia, periorbital oedema.
• Diagnostics: Muscle biopsy, serology.
• Treatment: Albendazole/mebendazole + steroids if severe.

Dracunculus medinensis (Guinea Worm)

• isolated cases in Chad/Ethiopia
• Transmission: Drinking water with copepods carrying larvae.
• Clinical: Painful skin ulcer with emerging worm.
• Diagnostics: Clinical.
• Treatment: No drug; slow extraction of worm. WHO eradication programme.

Toxocara canis/cati

• Transmission: Ingestion of dog/cat roundworm eggs.
• Clinical: Visceral larva migrans, ocular larva migrans.
• Diagnostics: Serology (ELISA), eosinophilia.
• Treatment: Albendazole ± steroids.

Filarial worms

• Wuchereria bancrofti / Brugia malayi
  • Geography: Africa, Asia, Pacific, India.
  • Transmission: Mosquito bite.
  • Clinical: Lymphatic filariasis → elephantiasis.
  • Diagnosis: Peripheral films
  • Treatment: DEC + albendazole.
• Loa loa
  • Geography: West and Central Africa (rainforest belt).
  • Transmission: Chrysops fly (day-biting).
  • Clinical: Calabar swellings, migrating eye worm.
  • Treatment: DEC (caution with high microfilarial loads).
• Onchocerca volvulus
  • Geography: Sub-Saharan Africa, Yemen, Central/South America (riverine areas).
  • Transmission: Blackfly (fastflowing riverine areas).
  • Clinical: River blindness, dermatitis, hanging groin.
  • Diagnostics: Skin snip microfilariae.
  • Treatment: Ivermectin (DEC contraindicated due to Mazzotti reaction).

4. Tissue Nematodes (Zoonotic)

Anisakis spp.

• Epidemiology: Japan, raw/undercooked marine fish.
• Clinical: Acute abdominal pain (gastric anisakiasis).
• Diagnostics: Endoscopy (larva).
• Treatment: Endoscopic removal.

Capillaria philippinensis

• Transmission: Ingestion of raw freshwater fish.
• Epidmiology: Phillipines, Thailand
• Clinical: Malabsorption, chronic diarrhoea, wasting.
• Treatment: Albendazole.

🔑 Extra Exam Pearls

• Eosinophilia → classic for tissue-migrating helminths (schistosomes, strongyloides, filariae, trichinella, toxocara).
• Cancer links → S. haematobium (bladder), Clonorchis/Opisthorchis (cholangiocarcinoma).
• Treatment pitfalls →
  • Fasciola → triclabendazole (not praziquantel).
  • Strongyloides → ivermectin (not albendazole).
  • Onchocerca → ivermectin (not DEC).
• Public health →
  • Schisto MDA with praziquantel.
  • Filariasis elimination with DEC + albendazole.
  • Guinea worm near-eradication.
• Diagnostics → stool/urine microscopy, serology, antigen tests, PCR, imaging (hydatid, neurocysticercosis).
• Other → Echinococcus cysts (risk of anaphylaxis), Strongyloides hyperinfection in immunosuppressed.